First up, the new GTK+ 3.13.6 release has been updated to support newer versions of the Wayland protocol. Beyond that as the only Wayland change for this GTK+ 3.14 development release, there's Adwaita theme improvements, a faster blur implementation for shadows, and a variety of other GTK improvements. There's a total of 37 known bug-fixes in the GTK+ 3.13.6 release.
All the GTK+ 3.13.6 details can be found via the news item.
GNOME 3.14 is due for its official release on 24 September while coming up next week (20 August) is the planned GNOME 3.14 Beta (v3.13.90). Earlier GTK+ changes this cycle included a new default theme and other Wayland improvements.